1. Field of the Invention
The present invention relates to a process for producing methacrolein by a vapor phase catalytic oxidation of isobutylene or tertiary butanol. More particularly, it relates to a process for producing methacrolein by a vapor phase catalytic oxidation of isobutylene or tertiary butanol in the presence of a novel complex oxide catalyst comprising components of Mo, Co, Fe, Bi, Tl, V and/or Nb, if necessary, La and/or Ce, Cs and/or Te.
2. Description of the Prior Arts
The processes for producing unsaturated aldehydes such as acrolein or methacrolein by vapor phase catalytic oxidations of lower .alpha.-olefins such as propylene or isobutylene, have been proposed in many patent applications. In most of the cases, complex oxide catalysts comprising components of Mo, Co and/or Ni, Fe and Bi and other elements have been used. Various additional elements have been proposed as described in Japanese Unexamined Patent Publication No. 34107/1976, and No. 40,391/1976, etc.
In order to increase selectivity of the object compound of the unsaturated aldehyde, it has been known that the incorporation of thallium is effective for the oxidation of isobutylene. Furthermore, it has been proposed to incorporate an alkali metal component such as K, Rb and Cs, or the other component of P, As, B or Sb.
The incorporation of these component may improve the selectivity, but may decrease the activity. In some cases, the decrease of the activity is caused during the reaction. Thus, these processes have not been always satisfactory. In view of industrial operations, it is important to give high selectivity in high conversion, that is, high catalytic function for high per-pass yield. The inventors have studied on the improvement of the catalysts.